1. Field of the Invention
The present invention relates to a transmission line interconnecting system which interconnects two transmission power lines so as to accommodate an active power between the two transmission lines during emergency period.
2. Description of the Prior Arts
In the conventional system controlling system, two pairs of line commutated type converters are connected in series in the DC side and the control between the converters has been carried out by controlling turn-on angles of thyristors. However, the power-factor of the converters has not been high and accordingly, about 60% of reactive power based on the converted active power should be fed during the power accommodation period. Moreover, when the power accommodation is not needed, this has not any effect to the power transmission line to be immaterial.
FIG. 1 is a connection diagram showing the principle of the conventional transmission line system. In FIG. 1, the reference numerals (1) and (2) designate respectively the first and second transmission lines; (3) and (4) designate respectively converters having thyristor circuits; (5) designates a smoothing inductor for controlling ripple current produced by the difference in voltage waveforms formed between the converters (3), (4). In the conventional transmission line system, the smoothing inductor (5) connected at the DC side of the converters (3), (4) carries out smoothing the DC current to form the AC current having rectangular waveform A current source inverter is formed by these parts. In the system, the active power from the transmission line is given as KEIa cos .alpha. and the reactive power from the transmission line is given as KEIa sin .alpha. wherein E designates a voltage in the transmission line; Ia designates AC current; and .alpha. designates a turn-on angle of the thyristor and K is a constant. These powers are respectively fed into the converters.
A ratio of the reactive power to the active power is given as sin 30.degree./cos 30.degree.=0.58 when .alpha. is 30.degree.. Thus, in the conventional transmission line, the reactive power is consumed from the system. Therefore it is necessary to have a phase adjusting device having large capacity, disadvantageously.